The subject matter of the present invention relates to a fully automated software based method and apparatus for 3D modeling of faulted geologic horizons, and more particularly, to a workstation based apparatus and associated software based method for modeling, in 3D space, a horizon in an earth formation which is intersected by one or more faults in the earth for the purpose of accurately determining the geometry of earth formations and consequently of a precise definition of oil reservoirs, the workstation generating, on a recording medium, a "final faulted horizon model" including a set of "final fault locations" which represent the intersection between the horizon and the fault(s), the generated "final faulted horizon model" assisting an operator interpreter in the task of locating underground deposits of hydrocarbons which are situated near the "final fault locations". A geologic horizon is the interface between two depositional earth formations or layers, which, when faulted, results in a complex interface with abrupt changes in depth.
The energy industry is continuously involved in the location of underground deposits of hydrocarbons, such as oil, in earth formations. In order to locate such hydrocarbons, "computer modeling" is a technique that is used for the purpose of simulating the earth formation in which the underground deposits of hydrocarbons are located. The earth formation is comprised of a plurality of horizons and a multitude of faults which intersect the horizons. When the computer modeling technique is used, a computer workstation executes a block of software and, in response thereto, a model is generated by a recorder that will contain horizon surfaces and will display all the intersections between all the faults and each of the horizons in the earth formation. The intersection between each fault and each horizon is called a "final fault location" and each horizon surface model that is generated by the workstation recorder is called a "final faulted horizon model". When the final fault locations on the final faulted horizon model are generated by the recorder, a workstation operator can determine the location of the underground deposits of hydrocarbon (e.g, oil) because the hydrocarbon deposits can be situated adjacent to one or more of the intersections (final fault locations).
However, in the past, the workstation operator had to arduously perform a significant amount of work in order to construct accurate faulted horizon models and determine the intersections (final fault locations) between the faults and each of the earth formation horizons. That is, when a horizon is intersected by a fault, in the past, a first section of the horizon located on one side of the fault had to be manually defined and extended by the workstation operator and a second section of the same horizon located on the other side of the fault also had to be manually defined and extended by the workstation operator in order to ultimately determine the shape and/or characteristics of the intersection (final fault location) between the fault and the horizon. This task performed by the operator is very laborious and time consuming, typically requiring many weeks, even months, to complete.
A common approach to construction of these types of models is to require at least partial definition of fault intersection lines as input along with horizon data. Older, more conventional modeling methods require definition of all intersection lines with no direct usage or requirement of faults as surfaces. The definition of these lines is typically done manually by the operator. Such definitions result in large errors which deteriorate the consistency and accuracy of all subsequent models. Less common, but more advanced, approaches take as an input fault geometry local to the horizon in the form of piecewise planar approximations, or they may accept faults as surfaces but with an additional requirement of approximate intersection lines to assist model building. Again, such operator defined output data is not guaranteed to be accurate and consistent with the rest of the input data which can corrupt the subsequent modeling results. Finally, there are other, even more advanced, approaches which are fully fault surface based, but lack automation, requiring time consuming human intervention and analysis at key phases of the modeling process.
In addition, the prior art horizon modeling system adapted to generate a final faulted horizon model utilized the "fault blocking" method. That is, for a particular horizon in the earth formation which is intersected by a plurality of faults to form a horizon model and a corresponding plurality of horizon/fault intersections on the particular horizon, a preliminary step was taken during the horizon modeling including the step of manually extending the ends of the horizon/fault intersections to the model boundary, or to another horizon/fault intersection, to thereby form a plurality of closed "fault blocks" on the particular horizon prior to performing the remaining horizon modeling steps and generating the final faulted horizon model. This preliminary step (of extending the ends of the horizon/fault intersections to the model boundary or to another horizon/fault intersection thereby forming the plurality of the fault blocks on the horizon) represents one type of design philosophy associated with one type of horizon modeling system, which design philosophy is different than the design philosophy of the horizon modeling system of the present invention. A fundamental assumption for all faulted horizon modeling methods is that the fault models are computed and available. Each model is represented by a surface in the 3D space. Every fault has a type associated with it (i.e., normal, reverse, mixed). A fault is "normal" if the horizon sections on both sides of the fault surface are non-overlapping. A fault is "reverse" if the horizon sections are overlapping. A fault is "mixed" if, in some areas along the fault surface, it is normal and, in others, it is reverse. We further assume that appropriate geological relationships between related faults are established and available (see prior pending application Ser. No. 08/823,107 filed Mar. 24, 1997 and entitled "Method and Apparatus for Determining Geologic Relationships for Intersecting Faults", the disclosure of which is incorporated by reference into this specification).
As a result, a fully automated general method and apparatus is needed in order to determine the shape and/or characteristics of each of the horizons and of each of the final fault locations (intersections) between each of the faults and each of the horizons in the earth formation. The requirement to form closed fault blocks for the definition of the faulted horizon model is eliminated completely. Thus, complicated faulted horizons can be constructed much more accurately and reliably in a very efficient way.